Method of bleaching cellulose wood-pulp.



UNITED STATES PATENT OFFICE.

FREDERICK WILLIAM DOBSOLLOF TAMWOBTH, ENGLAND.

- METHOD OF BLEAGHING CELLULOSE WOOD-PULP.

No Drawing.

Patented July 21, 1914;.

To all whom it may concern:

Be it known that I, F nnnnnron WILLIAM DoBsoN, a subject of the King of Great Britain and Ireland,- and resident of Tamworth, Staifordshire, England, have invented a certain Improved Method of Bleaching Cellulose Wood-Pulp, of which the following is a specification.

This invention refers to the bleaching of wood pulp fiber as used in paper making.

and commercially known as chemical Wood cellulose, which is wood treated by chemical reducing agents. Usually chemical wood cellulose is bleached in large open troughlike vessels, the cellulose, which is in sheet form, being first broken up and then placed,

along with a supply of water to soften it, into the bleaching vessels. To the cellulose is added the bleaching liquor which is in a dilute form, there beinga large excess of Water. are then circulated around and around the vessels until the cellulose is fully bleached. The drawbacks to this method of bleaching are that the time taken for bleaching is usually very considerable; that owing to the vessels being open the pulp is liable to get contaminated with dirt, etc; that the fumes from the bleaching materials, which are injurious to health, are free to escape into the atmosphere; that the bleaching materials cannot beregulated to any degree of nicety for a given bleach and that the cellulose, after bleaching, requires to be passed through drainer-s todrain 0d the surplus liquor before it can pass to the heaters, this latter being a serious drawback when rapidity of output is of first importance.

This invention has for its objecta method of bleaching chemical wood cellulose Whereby the aforesaid drawbacks are overcome, and especially in respect to the bleaching of the same quantity of pulp in less time than heretofore and also in respect to dispensing with the need to drain the cellulose after being bleached and before passing to the boaters.

According to the invention, the improved bleaching operation is carried out in a closed vessel, preferably of drum formation, and capable of'being rotated. Usually an iron or steel vessel similar to a horizontal keir will be used, the vessel being supported horizontally by trunnions rotating in fixed bearings. Upon its interior the vessel may The cellulose and bleaching liquor facin or lining capable of protecting the vesse from the action of the bleaching liquor. This lining is notstrictly necessary and may be omitted. Into such vessel, which is provided with suitable manholes, is placed the cellulose and bleaching solution. In practice it is found best to first run the supply of bleach liquor which is in a concentrated form, into the vessel, and then the water necessary for producing the desired bleaching solution. To this solution is then dry sheet form. That is to say, the cellulose is not previously broken up and is quite dry when introduced into the vessel, no moisture of any kind having been applied to it. The bleaching material will be chloquantities of cellulose and bleaching solution, the vessel is slowly and continuously rotated, thereby causing the cellulose and bleaching liquor to become thoroughly intermixed and the desired bleaching operation to be effected in a comparatively short time. The rapid bleaching operation is largely due "to the cellulose being in a dry form on the bleaching liquor coming in contact With it, whichv enables the bleaching material to rapidly penetrate the cellulose. In other words, the cellulose in a dry state rapidly absorbs moisture and by this invention advantage is taken of such fact to bring about the rapid bleaching operation.

A vessel suitable for the purpose of the invention may be 24 feet long by 7 feet diameter, suit-able pulleys or gearing being provided for transmitting rotary motion to the vessel.

There are different kinds of chemical wood cellulose but this invention is concerned chiefly with sulfite cellulose and soda cellulose sold unbleached for bleaching.

tions of concentrated bleaching liquor, water and cellulose for a complete bleach have been found to give the most satisfactory results, viz:

(a) 2 tons of sulfite cellulose, 435 gallons of bleaching liquor (5% to 6 Twaddell), 1000 gallons of water. This represents 4.8 lbs. bleaching powder to 100 lbs. of dry cellulose.

(b) 30 cwt. of soda cellulose, 690 gallons of bleaching liquor (5 to 6-Twaddell),

be faced or lined with cement, tiles on other rid of lime. When charged with the proper The following examples of the proporadded the cellulose which is, preferably, in

630 gallons of water. This represents 10.2 lbs. bleaching powder to 100 lbs. of dry cellulose.

It is to be noted that soda cellulose expends on absorption with water more than 'sulfite cellulose and consequently reduces l the cellulose, the presence of any water previously added to the cellulose being detrimental to the rapid action of the bleaching liquor. For the quantities before named and the size of vessel indicated the bleaching of the cellulose is completed in about 3 hours, the vessel being rotated about 2 to 42 revolutions per minute.

After being bleached the cellulose is removed from the vessel through a manhole or manholes direct into tubs or other receptacles by which it may be conveyed to the heaters. That is to say, owing to a con centrated bleaching liquor being used and also owing to only so much bleaching liquor being used as is necessary, there is no need for the bleached cellulose to be submitted to a draining operation, the bleached cellulose being in a condition suitable for direct transference to the heaters. It should now be seen that by reason of the rapidity and exactitudc with which the bleaching operation can be performed and further by reason of the entire absence of the need. for drainers considerable advantages are obtained over and above the ordinary method of treatment. Moreover, the plant and power required for bleaching a given quantity of pulp in a given time are much less from the vessel is practically free from smell. Further by treating the cellulose in sheet form the labor of breaking it up as heretofore necessary is avoided, and much time thus saved. It will be understood that the amount of bleaching material used Will depend on the degree of whiteness required.

The bleaching vessel will be driven by any suitable form of motor and the direction of its rotation may, by suitable reversing gear, be periodically reversed to insure of the most effective action of the bleaching liquor. Suitable provision may be made for indicating the contents of the vessel, and also for indicating the speed of the vessel.

What I claim is:-

The herein described process of bleaching chemical wood cellulose which consists in placing a concentrated bleaching agent in a rotary vessel, adding water thereto to form. a solution, placing within the vessel the cellulose to be bleached in sheet form and dry, and rotating the vessel, the amount of the bleaching solution being so proportioned with respect to the amount of cellulose to be bleached as to render subsequent draining of the bleached cellulose unnecessary.

In witness whereof I have hereunto set my hand in the presence of two witnesses.

FREDERICK WILLIAM DOBSON.

"Witnesses:

KATHLEEN MARY THOMPSON, -ERNES1 HARKER. 

